Messages in this thread | | | Date | Mon, 12 Jul 2021 16:50:44 +0800 | From | Boqun Feng <> | Subject | Re: [RFC PATCH v1 1/3] locking/lockdep: Fix false warning of check_wait_context() |
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On Mon, Jul 12, 2021 at 04:18:36PM +0800, Xiongwei Song wrote: > On Mon, Jul 12, 2021 at 12:43 AM Waiman Long <llong@redhat.com> wrote: > > > > On 7/11/21 10:14 AM, Xiongwei Song wrote: > > > From: Xiongwei Song <sxwjean@gmail.com> > > > > > > We now always get a "Invalid wait context" warning with > > > CONFIG_PROVE_RAW_LOCK_NESTING=y, see the full warning below: > > > > > > [ 0.705900] ============================= > > > [ 0.706002] [ BUG: Invalid wait context ] > > > [ 0.706180] 5.13.0+ #4 Not tainted > > > [ 0.706349] ----------------------------- > > > > I believe the purpose of CONFIG_PROVE_RAW_LOCK_NESTING is experimental > > and it is turned off by default. Turning it on can cause problem as > > shown in your lockdep splat. Limiting it to just PREEMPT_RT will defeat > > its purpose to find potential spinlock nesting problem in non-PREEMPT_RT > > kernel. > As far as I know, a spinlock can nest another spinlock. In > non-PREEMPT_RT kernel > spin_lock and raw_spin_lock are same , so here acquiring a spin_lock in hardirq > context is acceptable, the warning is not needed. My knowledge on this > is not enough, > Will dig into this. >
You may find this useful: https://lwn.net/Articles/146861/ ;-)
The thing is that most of the irq handlers will run in process contexts in PREEMPT_RT kernel (threaded irq), while the rest continues to run in hardirq contexts. spinlock_t is allowed int threaded irqs but not in hardirq contexts for PREEMPT_RT, because spinlock_t will become sleeplable locks.
Regards, Boqun
> > The point is to fix the issue found, > Agree. I thought there was a spinlock usage issue, but by checking > deactivate_slab context, > looks like the spinlock usage is well. Maybe I'm missing something? > > > not hiding it from appearing. > I'm not trying to hiding it, according to the code context, the fix is > reasonable from my point of > view. Let me check again. > > Thank you for the comments. > > Regards, > Xiongwei > > > > Cheers, > > Longman > >
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